To go back to the originaql question - "what is a lift kit?"
When a TM is built, the frame (the body) of the trailer rests on the axle assembly. A "lift kit" is simply a spacer that goes between the two, and lifts the body of the trailer a couple inches further off the axle, and hence a couple inches further off the ground.
As noted in previous responses, there are a couple reasons to do this. One is to lessen the likelihood that the body of the TM will drag on the ground when exiting a gas station or travelling over rough ground,. Another is to increase the clearance above the tire so that a larger tire can be used.
When a lift kit is used to raise the trailer further off the ground, it also raises the center of gravity of the trailer, which is not always a good thing. As usual, there are tradeoffs.
I seem to recall that Bill Miller from Houston posted a good description and some good pictures. Try here
http://www.trailmanorowners.com/foru...ad.php?t=12132
Bill